Searching for a counterfeit coin with two unreliable weighings

Authors:
Wen-Au Liu;Qi-Min Zhang;Zan-Kan Nie
Affiliations:
Faculty of Mathematics and Information Science, Henan Normal University, Xinxiang, PR China;Faculty of Mathematics and Computer Science, Ningxia University, Yinchuan, PR China;Faculty of Science, Xi'an Jiaotong University, Xi'an, PR China
Venue:
Discrete Applied Mathematics - Special issue: Max-algebra
Year:
2005

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Abstract

We provide a worst-case optimal procedure to identify one unknown heavy coin among N identically looking coins when a balance scale is used and at most two weighing results can be erroneous. The exact minimal number of weighings is determined. This solves completely the weighing problem of the case of two unreliable weighings.